1. Field of the Invention
Embodiments of the invention relate to improvements in pumping fluids from tanks or other supplying vessels. Specific aspects of the invention, for example, relate to pumping propane from a vehicle, such as a bobtail or tank truck, with improvements in e.g. thermal characteristics and pump operation. Other examples will be described as well.
2. Description of Related Art
Liquefied compressed gases such as propane are generally transported via truck primarily in two different ways. The first way is via a transport. A transport is a trailer that holds approximately 7,000-10,000 gallons of liquid propane. The transport is used to fill outlying storage tanks and large industrial tanks. The second way is via a straight truck, which the propane industry typically calls a bobtail. The bobtail typically holds less than 3,500 gallons of liquid propane and is used to fill residential and small business propane tanks.
When a transport unloads, the operator generally will connect two hoses between the transport and the storage tank. The first hose connected is called the vapor hose and the second is called the discharge hose. The purpose for the vapor hose is to allow the vapor pressures between the transport and the storage tank to equalize and to allow vapor pressure to be pushed back into the transport vapor space while they are pumping. This equalizes the pressures and allows the liquid product pump to pump at a higher rate and lower pressures, which minimizes noise and internal damage to the propane pump.
When a bobtail unloads, the operator typically uses only a discharge hose. Most bobtails do not have a second vapor hose. Not having the vapor hose causes two things to happen. First, as the propane pump on the bobtail pumps liquid propane from the bobtail into the storage tank, the pressure in the storage tank continues to rise and causes back pressure on the discharge line. This back pressure causes the discharge line pressure to continue to rise, causing the pump to work harder and thus reducing the flow rate and increasing the wear of the propane pump. Second, as the propane pump pulls product out of the bobtail tank it creates a vacuum inside the bobtail tank. This vacuum creates bubbles in the propane which are then pulled through the propane pump. As these bubbles are pulled through the propane pump they compress and then expand rapidly, potentially causing damage to the internal vanes and rotor of the propane pump. These bubbles reduce the flow rate of the pump and create a higher level of pump noise.
Liquid products that do not change state as readily, such as fuel oil and refined fuel, are transported via truck primarily in two different ways. The first way is via a transport, described earlier. The second way is via a straight truck. The straight truck carries 500-5,000 gallons of product. The straight truck typically delivers to residential customers and to small industrial customers.
With liquid products that do not change state, both the transport and the straight truck unload in approximately the same way. The operator connects a single discharge hose between the transport or straight truck to the storage tank. Once this has been accomplished, the operator then starts the pump and pumps the liquid product into the storage tank. Since this type of liquid is not pressurized to maintain it as a liquid, the transport, straight truck and storage tanks can all be vented to atmosphere. This eliminates the need for a vapor hose.
Thus, the propane bobtail delivery market and the fuel-oil and refined-fuels tank-truck delivery market, for example, are similar in that typically they both use a tandem-axle-style truck with a multi-thousand gallon tank mounted on the chassis. These vehicles are used to deliver typically small quantities of e.g. propane, fuel oil, diesel fuel and gasoline to e.g. homes, farms and small businesses.
Currently, there is a movement in these industries to change from driveline-driven product pumps to hydraulic drives. This change is coming from a number of areas, e.g. safety, maintenance and a need to either mount the product pump in a location that cannot be easily driven by a driveshaft or a need for two or more product pumps on a truck. The tank-truck market is shifting towards having larger and multicompartment tanks on their trucks. This shift allows more efficient use of their trucks and their employees.
It would be desirable to take advantage of the movement to change from driveline-driven product pumps to hydraulic drives, to further capitalize on the attendant advantages. Additionally, a need exists to diminish the problems of back pressure and vacuum-induced bubbles in e.g. propane, which bubbles are then pulled through the propane pump. It would also be desirable to diminish the disadvantages caused by using a fan for cooling, e.g. noise, vibration/resonance, and maintenance/upkeep concerns.
To achieve the above and other goals, one embodiment of the invention uses the product that the customer is pumping, e.g. propane, to cool the hydraulic oil used to run the pump. A liquid-to-liquid heat exchanger receives the hydraulic oil line and a line containing the pumped product. Approximately two gpm of product can be pumped through the heat exchanger, according to one embodiment. The two liquids are separated by thin channels of e.g. stainless steel or another material. The heat exchanger cools the hydraulic oil and warms the customer""s liquid product. Embodiments of the invention have particular advantages in e.g. the propane industry. Propane is heated, vaporized and then pumped back into the top of the supplying tank. This vaporized propane increases pump flow rates, reduces cavitation and increases pump life. These advantages are obtained, according to embodiments of the invention, with no fan motor, better product pump performance, longer product pump life, and smaller and lighter pump weights.
The theory behind embodiments of the invention is twofold for e.g. propane types of application. First, by using the liquid propane as the cooling agent inside the liquid-to-liquid heat exchanger, the hydraulic oil is kept at a safe operating temperature without the use of a cooling fan. Second, as the hydraulic oil passes through the heat exchanger it heats the liquid propane.
The heated liquid propane is boiled or vaporized and then pumped back into the vapor space, or liquid space, in the bobtail tank. By reintroducing this vapor back into the bobtail tank, the problems that were stated above are minimized. Embodiments of the invention decrease the length of time during which product can be unloaded, stabilize the vapor pressure in the bobtail tank, reduce pump wear and noise, and cool the hydraulic system without the need for any type of cooling fan.
Embodiments of the invention for liquid products that do not as readily change state regulate a small amount of the liquid product being pumped through the heat exchanger. As the liquid passes through the heat exchanger, it cools the hydraulic oil. The heated liquid product is the reintroduced back into e.g. either the transport or straight truck tank or back into the discharge line of the pump.
Embodiments of the invention provide significant advantages, in that they can cool the hydraulic oil without the need for a cooling fan and can aid in the pumping of liquids that become more difficult to pump in colder climates.
Embodiments of the invention can be described as a combination of a hydraulic oil cooler and a supplying vessel pressure stabilizer. Embodiments of the invention can be used in applications that require hydraulic oil to be cooled while it is operating a product pump that is pumping some type of liquid product. The hydraulic oil is cooled via a xe2x80x9cliquid-to-liquidxe2x80x9d heat exchanger, for example. This heat exchanger can have up to at least three channels allowing up to at least three different liquids to pass through it at any one time.
On one side of the heat exchanger is the hydraulic oil and on the other side(s) are one or more liquid products that are being pumped by the product pump(s). The liquid products absorb the heat of the hydraulic oil. In effect, embodiments of the invention are cooling the hydraulic oil and heating the amount of liquid product that is being pumped through the heat exchanger. This device will work when the temperature of the liquid product being pumped is less than the maximum desired hydraulic oil temperature. Different types of liquids at different flow rates affect the cooling capacity of the heat exchanger and the amount of heat being transferred into the liquid product being pumped. Hydraulic oil flow rates at varying pressures affect the amount of heat (BTU""s) that are produced.
At least two different types of liquid products can be used with this device. The first is a xe2x80x9cnon-state-changingxe2x80x9d liquid, as referenced above. This type of liquid does not change its state when the amount of heat (BTU""s) that a hydraulic system creates is dissipated and absorbed by the liquid. For example, embodiments of the invention simply add a fixed amount of BTU""s to diesel fuel. These added BTU""s increase the temperature of the diesel fuel to a predetermined and controlled safe temperature. The second type of liquid, the xe2x80x9cstate-changingxe2x80x9d liquid, begins to boil or vaporize as its temperature is changed. These types of liquids are typically referred to as liquefied compressed gases. For example, propane will boil or vaporize as heat is introduced to it.
According to embodiments of the invention, the liquid product being pumped through the heat exchanger is reintroduced back into the supplying vessel once it has circulated through the heat exchanger. Depending upon the product, it will enter back into the supplying vessel as a warmed-up liquid or as a boiling liquid or vapor. This vapor can be extremely beneficial to certain types of supplying vessels to aid in the pumping process. This benefit will be described in detail, further into this description.
Embodiments of the invention contain a xe2x80x9cliquid-to-liquidxe2x80x9d heat exchanger, a hydraulic reservoir, and a hydraulic oil filter. These parts are manufactured and assembled into a package that is compact, light-weight and easy to install for the customer. Embodiments of the invention also diminish many of the problems referenced above, e.g. back pressure, vacuum-induced bubbles, cavitation, noise, vibration/resonance, maintenance/upkeep concerns, and the like.
Additional features and advantages according to embodiments of the invention will become apparent from the remainder of this patent application.